Now I am working on updating the user interface of my application (XF for Android). I found this solution for the application interface (from the Evolve 2016 source code ):

It looks beautiful and is implemented simply:
<ContentPage.Content>
<Grid RowSpacing="0" >
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackLayout BackgroundColor={StaticResource Primary}, Grid.Row=0/>
<SearchBar/>
</StackLayout>
<StackLayout Grid.Row=1>
//other content
</StackLayout>
.....
For existing navigation (Master-Detail), it works great. But I click on an element (on this page) - than I open a new page (there is no basic information). Work as follows:
await Navigation.PushAsync(new SessionDetailPage(), true);
I click on the toolbar - I return to the session page, than for a short time the white line

it does not last long, second second. then the white line disappears. But it is unpleasant to use. Any ideas? How can I improve this?